This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-170037, filed Jun. 16, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a distance measuring apparatus for the camera that adopts a so-called hybrid type autofocusing (hereinafter referred to as AF) which uses active type AF and passive type AF jointly.
There is a remarkably progress in a technology for the AF, whereby focusing is carried out automatically, in line with a trend in cameras toward automatization.
Such AF technologies can be divided broadly into two categories: the passive method where mainly an image signal of a subject is utilized; the active method where light is cast from a camera and the reflected light signal is detected.
In the passive type AF, light-converted signals which are outputted by sensor arrays are converted from analog signals to digital signals through A/D conversion, and further the digital signals so obtained are put into arithmetical operations. Therefore, a number of steps such as integration control, designation of an area or areas, cross correlation calculation for detecting coincidence of images are necessary, especially in a dark scene a longer time is required to integrate photocurrent, resulting in distance measurement with a long time lag. Moreover, accurate distance measurement was not able to be performed if the obtained image signals do not have enough contrast.
On the contrary, in the active type AF, since light is cast on the subject and reflected light from the subject is received to perform distance measurement; the active type AF is hard to be affected by the luminance of the subject and further said to be suitable to measure a subject with low contrast.
In consideration of such features of the two type of AFs, in the Japanese Unexamined Patent Application Publications No. 48-52231 and No. 55-35399, disclosed are technologies where the active type AF is used jointly with the passive type AF under conditions of low luminance, low contrast, etc. with the aim of compensating week points peculiar to the passive type AF as described above.
Further, in the Japanese Unexamined Patent Application Publications No. 9-5611, disclosed is a technology for a distance measuring apparatus where the AF is normally carried out by both the active type AF and the passive type AF, but when a night scene-shooting mode is set, the AF operation in a passive distance measuring part is disabled by the control of a CPU and only an active distance measuring part is allowed to carry out the AF.
In the Japanese Unexamined Patent Application Publications No. 11-83474, disclosed is such a technology for a distance measuring apparatus that, when a taking lens is set to wide-angle, the active type AF is carried out, and when the lens is set to telephoto, the passive type AF and the active type AF are carried out simultaneously.
However, although the active type AF has a feature of being suitable for low-contrast and low-luminance scenes, it has a drawback that correct distance measurement cannot be performed in cases where no reflected signal light comes back to the camera, that is, camera-to-subject distance is too far or the reflectance of the subject is too low. A problem concerning which type AF should be chosen from the two types each having different features to achieve better focus is very difficult to decide, and if a distance measuring apparatus takes too much time for its choosing, a shutter time lag associated with this idle time may cause loss of a shutter chance. Moreover, a technology whereby a distance measuring method is changed in accordance with the change of a shooting mode, as disclosed in the Japanese Unexamined Patent Application Publication No. 9-5611 for a distance measuring apparatus, needs an operation of a photographer beforehand; therefore the concept of this technology is quite different from an idea of full automatic operation.
As for the technology disclosed in the Japanese Unexamined Patent Application Publication No. 11-83474, it is difficult to say that this method can cope with every shooting conditions because only active type AF is carried out when the taking lens is set to wide-angle.
The present invention is accomplished in consideration of the problems and it is the object thereof to provide a distance measuring apparatus for the camera wherewith the camera can realize high-speed, accurate focusing in every shooting conditions by automatically deciding priority of two distance measuring methods, namely the active and passive methods, rapidly.
To achieve the object, in a first embodiment according to the present invention, provided is a distance measuring apparatus comprising:
first distance measuring means for performing distance measurement by casting distance measuring light on a subject and using reflected light from the subject; second distance measuring means by using an image signal of the subject; service condition detecting means for detecting a condition when the camera is being held; and controlling means for performing distance measurement by changing the first and second distance measuring means in accordance with an output of this service condition detecting means.
In a second embodiment according to the present invention, provided is a distance measuring apparatus for a camera having a plurality of distance measuring methods, being designated as first and second methods, comprising:
service condition detecting means for detecting the condition when the camera is being held; zooming detecting means for detecting a zooming condition of the camera; and controlling means for changing the distance measuring methods in accordance with the holding condition and the zooming condition.
In a third embodiment according to the present invention, provided is a distance measuring apparatus for the camera having a plurality of distance measuring methods, that is, the first and second distance measuring methods, comprising:
zooming detecting means for detecting the zooming condition of the camera; image signal detecting means for detecting the image signal of a subject; and controlling means for changing the distance measuring methods in accordance with a result of judging reliability of the image signal.
In the fourth embodiment according to the present invention, provided is a distance measuring apparatus for the camera having a plurality of distance measuring methods, that is, the first and second distance measuring methods, comprising:
zooming detecting means for detecting the zooming condition of the camera; and controlling means for changing a sequence of the first and second distance measuring methods in accordance with the zooming condition detected by this zooming detecting means.
In the fifth embodiment according to the present invention, provided is a distance measuring apparatus for the camera having a plurality of distance measuring methods, that is, the first and second distance measuring methods, comprising:
shooting condition detecting means for detecting a shooting condition; and controlling means for changing the sequence of the first and second distance measuring methods in accordance with the shooting condition detected by this shooting condition detecting means.
In the sixth embodiment according to the present invention, provided is a distance measuring apparatus for the camera comprising:
first distance measuring means for measuring a distance to a subject based on a signal generated when the distance measuring light was cast on the subject positioned at the center in a viewfinder picture frame and reflected light from the subject is received;
second distance measuring means for measuring a distance to the subject by using a light reception signal corresponding to an image of the subject;
focal distance information detecting means for detecting focal distance information of the taking lens of the camera;
controlling means capable of distance measurement by means of the first and second distance measuring means regardless of an output of the focal distance information detecting means;
characterized in that the controlling means changes the priority of the first and second distance measuring means in response to the output of the focal distance information detecting means.
In the seventh embodiment according to the present invention, provided is a distance measuring apparatus for the camera comprising:
condition detector sensor for detecting a condition when the camera is being held;
a light sensor for detecting light from the subject;
a controlling circuit for selectively changing a passive distance measuring mode where distance measurement is performed based on an image signal outputted from the light sensor and an active distance measuring mode where distance measurement is performed based on a reflected light signal outputted from the light sensor when light is cast on the subject and reflected light from the subject is received;
characterized in that the control circuit changes the passive distance measuring mode and the active distance measuring mode in accordance with the output of the above-motioned condition detector sensor.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.